In these studies, we are attempting to define the immunologic events which both contribute to and affect the ability of the host to produce mammary tumors. Through the use of thymectomy, cell transfer, and low dose irradiation manipulations, we are exploring the relationship which exists between the host and its neonatally transferred virus. By exploration of tumor cell MTV glycoprotein expression and host ability to respond immunologically to these antigens at various times in the life cycle, we hope to obtain a clear picture of the antigenic spectrum of natural immune response to MMTV. Exploration of types of cells involved in the immune response to MMTV, such as "natural" killer cells, T-killer, T-helper and T-suppressor cells and their antigenic specificities will allow us to more fully understand the type of genetic control involved in immune responsiveness to MMTV.